This invention relates to a device for retaining the corners of a bed sheet, blanket or other covering under the corners of a mattress. It is also useful for retaining other sheet-like products such as tarpaulins, tents, etc. A problem which occurs frequently with such bed coverings is that they become dislodged during use, which problem is especially the case with waterbed type mattresses, due no doubt to the vibration or similar movements which occur during use.
Various attempts have been made to solve this problem but even the use of sheets designed to be fitted over mattress corners has not been fully satisfactory, especially in the case of waterbed mattresses. Certain mechanical retainers have been utilized such as shown in U.S. Pat. Nos. 4,400,836, 4,520,518 or 4,521,970. These devices have certain disadvantages in that they either require the use of clips or buttons affixed to retainers to be inserted under the mattress or in the case of U.S. Pat. No. 4,400,836, require the insertion of the corner of the sheet through a series of slots which in the construction described will still permit the corner to be withdrawn from the device under tension or vibration.